Hotter trend Climate change will trigger harsher and more frequent heat waves in the next 30 years regardless of the amount of Earth-warming carbon dioxide we emit, a study reveals.

But targets adopted today for curbing greenhouse gas emissions will determine whether the pattern stabilises thereafter, or grows even worse.

High temperatures and heat waves in the last decade are widely blamed on climate change that occurred over the last 50 years - amounting to global warming of about 0.5°C, according to the study in the journal Environmental Research Letters.

And they are predicted to become harsher and more frequent as the Earth continues to warm over the course of the 21st century.

In their study, Dim Coumou, from the Potsdam Institute for Climate Impact Research, and Alexander Robinson, from Universidad Complutense de Madrid used climate modelling to project extreme heat waves like those that hit Australia in 2009.

They found that extreme heatwaves will by 2020 affect about 10 per cent of total land area -- double today's figure. By 2040, it would have quadrupled.

"Over the same period, more extreme events will emerge: five-sigma events which are now essentially absent will cover a small but significant fraction (about three percent) of the global land surface by 2040," the researchers write.

Five-sigma events are described as "unprecedented" heat waves by the researchers and extreme events as three-sigma.

"In the first half of the 21st century, these projections will occur regardless of the amount of CO2 emitted into the atmosphere," according to a statement by the Institute of Physics which publishes the journal.

Beyond 2040

But what happens after 2040 can still be influenced by what we decide now.

"Under a low emission scenario, the number of extremes will stabilise by 2040, whereas under a high emission scenario, the land area affected by extremes will increase by one per cent a year" until three-sigma heat waves affect 85 per cent of the global land area by 2100 and five-sigma events about 60 per cent.

A low emission scenario would entail limiting the concentration of greenhouse gases in the atmosphere to 490 parts per million of CO2 equivalent before 2010, followed by a decrease, whereas the worst case scenario involves no change to current trends.

UN members have adopted a target of curbing warming to a maximum 2°C, and are negotiating a new treaty on carbon emissions targets that must be signed in 2015 and enter into force by 2020.

The negotiations have been slow and the yearly rise in emissions has led some scientists to conclude that warming of 3 or 4°C is probable by century's end.